The statement, posted on Islamist Web sites, addressed bin Laden as "the sheik" and said al-Zarqawi's Unification and Jihad movement "badly needed" to join forces with al Qaeda.

"We will listen to your orders," it said. "If you ask us to join the war, we will do it and we will listen to your instructions. If you stop us from doing something, we will abide by your instructions."

U.S. officials have said they believe the Jordanian-born al-Zarqawi is in the insurgent-held city of Falluja, west of Baghdad, and numerous American airstrikes have targeted buildings believed to house his followers in recent weeks.

Unification and Jihad has claimed responsibility for the killings of numerous Westerners in Iraq, including the recent slayings of two Americans and a Briton kidnapped in September.

At least two audiotapes have appeared on Web sites over the past several months that CIA officials have attributed to al-Zarqawi, in which he claimed credit for attacks on coalition forces.

On a tape in April, al-Zarqawi claimed credit for the bombing of the U.N. headquarters in Baghdad on August 19, 2003, that killed 22 civilians, including the U.N.'s chief envoy to Iraq, Sergio Vieira de Mello. (Full story)

He also is suspected in the bombing of the Jordanian Embassy in Baghdad two weeks earlier that killed at least 16 people.

On the most recent tape, in July, al-Zarqawi threatened to kill Iraqi interim Prime Minister Ayad Allawi; Gen. John Abizaid, commander of the U.S. Central Command in Iraq; and L. Paul Bremer, who was then the U.S. civilian administrator in Iraq.

Jordan and the United States suspect al-Zarqawi of planning the death of U.S. diplomat Laurence Foley, who was killed in October 2002 in Amman.

A Jordanian court convicted him in absentia of planning to bomb tourist hotels during millennium celebrations.

On Sunday, a Jordanian prosecutor indicted al-Zarqawi and 12 others on charges of plotting to attack targets in that country with chemical and conventional weapons.

In June, the U.S. State Department put a $25 million price on al-Zarqawi's head, saying he had "a long-standing connection to the senior leadership of al Qaeda." (Full story)

Officials have said al-Zarqawi, who is said to be skilled in chemical and biological weapons, is not known to have been a member of al Qaeda, but evidence suggests he was in contact with key figures of the terrorist network.

Other observers consider al-Zarqawi a potential rival to bin Laden, whose group was behind the terrorist attacks of September 11, 2001, in the United States.

Sunday's statement said al-Zarqawi has "exchanged views" with al Qaeda over the past eight months.

"[Al Qaeda] showed understanding for our strategy, and they showed their support for our strategy and style and system," the group's statement said.

Before the invasion of Iraq, U.S. intelligence reports suggested al-Zarqawi had his leg amputated in a Baghdad hospital after being wounded fighting U.S. forces in Afghanistan. The allegation was part of Secretary of State Colin Powell's presentation to the U.N. Security Council in February 2003, in which he laid out the U.S. case for war.

But in April, a senior U.S. official said that report had been called into question: al-Zarqawi was still thought to have received medical treatment in Baghdad, but reports that he had his leg amputated appeared to have been incorrect, a U.S. official said.

Powell held up al-Zarqawi's al Qaeda-affiliated group operating in Baghdad as evidence of ties between al Qaeda and Iraq. He told the Security Council that after al Qaeda and the Taliban were ousted from Afghanistan, al-Zarqawi established a camp in northeastern Iraq to train terrorists in using explosives and poisons.

Intelligence services disagreed whether the camp was linked to Saddam's regime, and Iraqi officials steadfastly denied they had any links to al Qaeda, insisting such charges were part of a U.S. disinformation effort to justify a military attack.

Powell said that during al-Zarqawi's stay in Baghdad, nearly two dozen of his associates set up a base of operations in the capital to move people, money and supplies throughout the country.